1. Field of the Invention
The invention relates generally to a motor, and more specifically to a motor including a damping member.
2. Description of Related Art
Damping members that are attached to motor housings in which motor bodies are housed are conventionally known. Such a damping member reduces the vibrations of a motor housing caused by the operation of a motor body. Examples of such damping members include damping members of unconstrained-type and damping members of constrained-type.
A damping member of unconstrained-type includes only a damping layer. The damping layer is disposed on a surface of a motor housing. The damping member of unconstrained-type converts vibration energy into thermal energy to reduce vibrations, using expanding deformation of the damping layer.
A damping member of constrained-type includes a damping layer and a constraining layer. For example, Japanese Patent Application Publication No. 2003-299300 (JP 2003-299300 A) describes a damping member of constrained-type including a damping layer and a constraining layer laminated on the damping layer. In the damping member, a surface of the damping layer is constrained by the constraining layer, so that the damping layer undergoes shear deformation. Thus, vibration energy is converted into thermal energy in the damping layer, whereby vibrations are reduced.
According to JP 2003-299300 A, the material of a constraining layer is preferably steel or aluminum. However, when a constraining layer is made of metal, it is difficult to uniformly bond a damping layer of a damping member to a motor housing that is not flat. Especially when appropriate bonding cannot be ensured between the damping layer and the motor housing, shear deformation of the damping layer is less likely to occur. As a result, vibrations of the motor housing are not effectively reduced, and high structure-borne noise may be generated.
In general, when a damping member is bonded to a motor housing, the damping member becomes a heat insulator and thus the temperature in the motor housing increases easily. In JP 2003-299300 A, the thickness of a damping member is set small to improve the efficiency of heat dissipation from the motor housing. However, it is difficult to achieve sufficient heat dissipation efficiency by adjusting the thickness of the damping member while maintaining sufficient damping performance.